Hughes XF-11 44-70155 at Culver City, California, 7 July 1946. The prototype Lockheed XC-69 Constellation, 43-10309, now registered NX67900, is in the background. Note the XF-11’s counter-rotating propellers. (University of Nevada, Las Vegas Libraries)
7 July 1946: At the Hughes Aircraft Company’s private airport in Culver City, California, the first of two prototype XF-11 photographic reconnaissance airplanes took of on its first flight. In the cockpit was Howard Robard Hughes, Jr.
Howard Hughes in the cockpit of the first prototype XF-11, 44-70155, with all propellers turning, at Culver City, California. (University of Nevada, Las Vegas Libraries)
The Hughes XF-11 was designed to be flown by a pilot and a navigator/photographer. Its configuration was similar to the Lockheed P-38 Lightning and Northrop P-61 Black Widow, as well as the earlier Hughes D-2. The prototype was 65 feet, 5 inches (19.939 meters) long with a wingspan of 101 feet, 4 inches (30.886 meters) and height of 23 feet, 2 inches (7.061 meters). The empty weight was 37,100 pounds (16,828.3 kilograms) and maximum takeoff weight was 58,300 pounds (26,444.4 kilograms).
Howard Hughes in teh cockpit of the XF-11 prototype. (Houston Chronicle)
The XF-11 was powered by two air-cooled, supercharged 4,362.49-cubic-inch-displacement (71.49 liter) air-cooled, supercharged Pratt & Whitney R-4360-31 (Wasp Major TSB1-GD) four row, 28-cylinder radial engines. This engine had a compression ratio of 7:1. It had a normal power rating of 2,550 horsepower at 2,550 r.p.m. at 5,000 feet (1,524 meters), and 3,000 horsepower at 2,700 r.p.m. for takeoff. The R-4360-31 was 4 feet, 4.50 inches (1.334 meters) in diameter, 9 feet, 6.25 inches (2.902 meters) long and weighed 3,506 pounds (1,590 kilograms). The engines drove a pair of contra-rotating four-bladed propellers through a 0.381:1 gear reduction.
The planned maximum speed was 450 miles per hour (724 kilometers per hour), service ceiling 44,000 feet (13,411 meters) and planned range was 5,000 miles (8,047 kilometers).
The first prototype Hughes XF-11, 44-70155, taking off from the Hughes Aircraft Company’s private airport, Culver City, California. 7 July 1946. (University of Nevada, Las Vegas Libraries)
After about an hour of flight, a hydraulic fluid leak caused the rear propeller of the right engine to go into reverse pitch. Rather than shutting the engine down and feathering the propellers to reduce aerodynamic drag, Hughes maintained full power on the right engine but reduced power on the left, attempting to limit adverse yaw to the right side.
Unable to make it back to the Culver City airport, Hughes planned to land at the Los Angeles Country Club. At 7:20 p.m., the airplane crashed into three houses on North Whittier Drive, Beverly Hills, California. The fire destroyed the prototype and one of the houses and heavily damaged the others. Howard Hughes was seriously injured in the crash.
Burning wreckage of Hughes’ prototype XF-11 in the yard at 808 N. Whittier Drive, Beverly Hills, California. (Los Angeles Times)Howard Hughes in an ambulance following the crash of the XF-11. (Los Angles Times)
The investigating board criticized Hughes for not following the flight test plan, staying airborne too long, and deviating from a number of standard test flight protocols. The cause of the actual crash was determined to be pilot error.
The second Hughes XF-11 landing at Culver City. (Los Angeles Times)
A second XF-11 was completed and flew in April 1947, again with Hughes in the cockpit. The project was cancelled however, in favor of the Northrop F-15 Reporter and Boeing RB-50 Superfortress, which were reconnaissance aircraft based on existing combat models already in production.
The second prototype Hughes XF-11, 44-70156, on a test flight near Anacapa Island, off the coast of Southern California, 1947. This airplane does not have counter-rotating propellers. (U.S. Air Force)
Martin XPB2M-1 Mars, Bu. No. 1520. (Hans Groenhoff Photographic Collection, Smithsonian Institution National Air and Space Museum NASM-HGC-1059)
3 July 1942: Chief Test Pilot William Kenneth Ebel, Ph.D., Vice President of Engineering for the Glenn L. Martin Company, took the Martin Model 170, s/n 877, for its first flight, lifting off from the waters of Chesapeake Bay. Dr. Ebel’s co-pilot was Ellis Dent Shannon, who would later become the chief test pilot for Convair.
Designated XPB2M-1 Mars, Bureau of Aeronautics serial number (“Bu. No.”) 1520, by the United States Navy, the flying boat was a prototype for a long-range patrol bomber. The first rivets had been driven for the airplane’s keel 22 August 1940, and the Mars was launched 8 November 1941. During a test in December 1941, the prototype had been damaged when a runaway propeller tore away from the No. 3 engine.
The Martin Mars prototype was launched 8 November 1941. (Charles M. Daniels Collection, San Diego Air & Space Museum Archives, Catalog #: 15_001975)
The U.S. Navy’s experiences early in World War II led it to adopt the Consolidated B-24 Liberator as its long range bomber (PB4Y-1 and PB4Y-2 Privateer). The XPB2M-1 was converted to a transport configuration, the XPB2M-1R, in 1943. The Navy ordered twenty transport versions, designated JRM-1. By the end of the war, only six had been built and the remaining order was cancelled.
Martin Model 170 Mars (XPB2M-1 Bu. No. 1520) at the Glenn L. Martin Co. ramp, near Baltimore, Maryland, 13 May 1942 (United States Navy, National Naval Aviation Museum, NMNA 1985.0481.003)
The Martin XPB2M-1 was a large, four-engine flying boat, operated by a crew of 11 persons. It was 118 feet, 9 inches (36.195 meters) long with a wing span of 200 feet, 0 inches (60.96 meters), and height of 37 feet, 4 inches (11.379 meters). The hull had a maximum width (“beam”) of 13 feet, 6 inches (4.115 meters). The total wing area was 3,683 square feet (342.2 square meters). The flying boat had an empty weight 75,573 pounds (34,279 kilograms), and gross weight of 140,000 pounds (63,503 kilograms).
The XPB2M-1 prototype was powered by four air-cooled, supercharged, 3,347.66-cubic-inch-displacement Wright R-3350-4 engines with a compression ratio of 6.85:1. Burning 100-octane aviation gasoline, these engines had a normal power rating of 1,700 horsepower at 2,300 r.p.m., and 2,000 horsepower at 2,400 r.p.m., at Sea Level for Takeoff. They drove three-bladed 16 foot, 6 inch (5.029 meters) diameter Curtiss Electric constant-speed propellers through a 16:7 gear reduction. The R3350-4 was 5 feet, 11.5 inches (1.816 meters) long, 4 feet, 7.12 inches (1.400 meters) in diameter, and weighed 2,450 pounds (1,111 kilograms).
The prototype Mars had a maximum speed of 221 miles per hour (356 kilometers per hour) at 4,500 feet (1,372 meters). It took 27.1 minutes to climb to 10,000 feet (,048 meters), and its service ceiling was 14,600 feet (4,450 meters). The flying boat’s fuel capacity was 10,410 gallons (39,406 liters), with 664 gallons (2,514 liters) of lubricating oil. This gave it a maximum range of 4,945 statute miles (7,958 kilometers)at 135 miles per hour (217 kilometers per hour). The maximum endurance was 37.1 hours at 131 miles per hour (211 kilometers per hour).
In the patrol bomber configuration, the XPB2M-1 could carry bombs or torpedoes. It was armed with machine guns for defense.
The XPB2M-1 was assigned to VR-8 at NAS Patuxent River, 27 Nov 1943, and later transferred to VR-2 at NAS Alameda. It was withdrawn from service in March 1945, and beached at Alameda. In April 1945 it was returned to Martin Co. for JRM-1 crew training. The prototype served as a maintenance trainer until 1949. It was then broken up.
The airplane once flew from PAX in the United States to Natal, Brazil, a distance of 4,375 miles (7,041 kilometers), while carrying a payload of 13,000 pounds (5,897 kilograms).
JRM: 0 -lift over drag coefficient 0.0233, max lift over drag 16.4
Martin Mars taxi test (Charles M. Daniels Collection, San Diego Air & Space Museum Archives, Catalog #: 15_001976)Martin Model 170 in flight. (Charles M. Daniels Collection, San Diego Air & Space Museum Archives, Catalog #: 15_001977)
Not So Graceful
It was not so graceful as it was towed from the Martin plant into the misty bay by small auxiliary craft.
Through the mists from following craft it looked like as large gray whale.
It was moved slowly by the power boats down Dark Head Creek from the plant and into the channel of the bay, 15 miles north of the mouth of the Patapsco River.
At the controls was William K. Ebel, chief test pilot and vice-president in charge of engineering at the Martin Company.
Maneuvered Slowly
He maneuvered the Mars slowly. When the towing boats cast off and while fireboats stood by, he started each engine separately.
It was at this point last December, during a water test, that the No. 3 propeller tore away.
No such mishap occurred yesterday. As the motors warmed, Ebel took the flying boat in half circles, first right, then left.
Then he “gunned” her and the Mars sailed through the water down the bay to meet boats carrying naval officials, executives of the Martin Company and Washington officials.
Twenty-Man Crew
With the twenty-man crew headed by Pilot Ebel, Co-Pilot Ellis E. Shannon, Capt. Harold Gray of Pan American Airways and Flight Engineer Benjamin Zelubowski, the ship warmed up for thirty minutes.
Brig. Gen. James H. Doolittle sat with Glenn L. Martin in the observer’s boat.
Out of the sky came a not-so-small navy amphibian plane. It paced the huge flying boat down the Chesapeake and hung over its right wing as the four largest propellers in the world lifted the ship from the water.
Together, the two planes disappeared toward the southwest. Within thirty minutes the Mars was back. It “bumped” easily four times and sat down just as easily in the water.
Martin Jubilant
Within a few minutes it was off again. This time it met the water evenly as it landed, then was immediately taken off again.
Its manufacturer, Glenn L. Martin, was jubilant over the flying boat’s maiden performance.
—The Sun, Baltimore, Maryland, Vol. 211, No. 42, Saturday, 4 July 1942, Page 18, Columns 3 and 4, and continued on Page 4, Column 6
Martin XPB2M-1 Mars with a 1941 Piper J3C-65 Cub, NC40743. (Hans Groenhoff Photographic Collection, Smithsonian Institution National Air and Space Museum NASM-HGC-1073)
William Kenneth Ebel was born at Orangeville, Illinois, 2 January 1899. He was teh son of Willam Henry Ebel, a farmer, and Nora Agnes Rubendall Ebel.
One 1 October 1918, Ebel was enlisted as a private in the Student Army Training Corps (SATC). He was trained at Heidelberg College, Tiffin, Ohio. With the end of the War, Private Ebel was discharged 20 Dec 1918.
Ebel continued his education at Heidelberg, graduating with a Bachelor of Arts (B.A.) degree in 1921, and in 1923, he completed a Bachelor of Science in Mechanical Engineering (B.S.M.E.) at the Case School of Applied Science, Cleveland, Ohio.
Also in 1921, Ken Ebel joined the 104th Observation Squadron, Maryland National Guard, based at Baltimore. He was assigned as an aviation cadet from 11 September 1923 to 3 June 1924. He was trained as a pilot at the National Guard Primary Flying School.
On 12 January 1925, William K. Ebel was commissioned as a second lieutenant, Air Service, Officers Reserve Corps. He was promoted to first lieutenant, Air Corps, 21 December 1926. He continued to serve with the Maryland National Guard
Also in 1926, Lieutenant Ebel began his career as an engineer and test pilot for the Glenn L. Martin Company.
Effective 15 February 1929, Ebel’s reserve officer’s commission was converted to first lieutenant, Air Corps.
On 21 October 1929, William Kenneth Ebel married Miss Florence E. Sherck at Seneca, Ohio. The would have two children.
Ebel was promoted to captain, Air Corps, 5 January 1935.
The first Martin Marauder, B-26-MA 40-1361, takes off for the first time at Middle River, Maryland, 25 November 1940. (U.S. Air Force)
On 25 November 19840, Ken Abel made the first flight of the Martin B-26 Marauder twin-engine medium bomber.
Ebel earned a doctorate degree in engineering (Ph.D.) from Case.
After the War, Ebel left Martin. In 1948, he became the director of the airplane division Curtiss Wright Corporation at Columbus, Ohio. In 1950 he was appointed vice president of engineering for Canadair Ltd., a Canadian aircraft manufacturer owned by the General Dynamics Corporation. After serving as a consultant for General Dynamics in Washington, D.C., Ken Ebel retired.
Mrs. Ebel died in 1968. He later married Ms. Helene H. Topping
Walter Kenneth Ebel died at the Greater Baltimore Medical Center, Baltimnore, 12 July 1972.
Bell 525 Relentless N525TA makes its first flight, 1 July 2015. (Bell Helicopter)
1 July 2015: Bell Helicopter’s new medium transport helicopter, the Model 525 Relentless, N525TA, made its first flight at Bell’s assembly plant in Amarillo, Texas. Test pilots Troy Caudill and Jeff Greenwood were in the cockpit.
The Bell 525 is the first helicopter to use fly-by-wire flight controls. Side stick controllers replace the customary cyclic and collective controls. For the first time for Bell, the 525 uses a five blade main rotor and four blade tail rotor.
Bell 525 Relentless prototype, N525TA.
The helicopter is designed to be operated by two pilots and carry up to 18 passengers. It is powered by two General Electric CT7-2F1 turboshaft engines, each rated at 1,714 shaft horsepower, maximum continuous power, and 1,979 shaft horsepower for takeoff.
N525TA during a test flight.
The Model 525 is the largest helicopter built by Bell. It has an overall length of 64.81 feet (19.75 meters) with rotors turning. The fully-articulated main rotor has a diameter of 54.50 feet (16.62 meters) and rotates counter-clockwise, as seen from above. (The advancing blade is on the helicopter’s right.) The mast tilts forward 5°. The four bladed tail rotor is mounted on the left side of a pylon and rotates clockwise when viewed from the helicopter’s left side. (The advancing blade is below the axis of rotation.) It has a diameter of 10 feet (3.05 meters). The pylon is canted to the left at 15°. The 525 Relentless has a maximum gross weight of 20,000 pounds (9,072 kilograms).
The Model 525 has a maximum cruise speed of 160 knots (184 miles per hour/296 kilometers per hour), and maximum range of 580 nautical miles (1,074 kilometers). At its maximum gross weight the helicopter can hover in ground effect (HIGE) at 10,700 feet (3,261 meters), and out of ground effect (HOGE) at 8,100 feet (2,469 meters).
The prototype Bell 525 Relentless, N525TA, in cruise flight. (Bell Helicopter)
N525TA was destroyed during a test flight approximately 30 miles south of Arlington, Texas, 11:48 a.m., 6 July 2016. While conducting a test to determine never exceed speed (VNE) for single-engine flight, the 525 was flying 185 knots (213 miles per hour/343 kilometers per hour) at 1,975 feet (602 meters), the main rotor blades “departed their normal plane of rotation” and struck the nose and tail. The two test pilots on board, Jason Cori Grogan and Erik Allan Boyce, were killed. Both were majors in the United States Marine Corps Reserve, assigned to HMLA 773. Each pilot was a graduate of the U.S. Naval Test Pilot School.
The National Transportation Safety Board (NTSB) determined that the Probable Cause was:
A severe vibration of the helicopter that led to the crew’s inability to maintain sufficient rotor rotation speed (Nr), leading to excessive main rotor blade flapping, subsequent main rotor blade contact with the tail boom, and the resultant in-flight breakup. Contributing to the severity and sustainment of the vibration, which was not predicted during development, were (1) the collective biomechanical feedback and (2) the attitude and heading reference system response, both of which occurred due to the lack of protections in the flight control laws against the sustainment and growth of adverse feedback loops when the 6-hertz airframe vibration initiated. Contributing to the crew’s inability to maintain sufficient Nr in the severe vibration environment were (1) the lack of an automated safeguard in the modified one-engine-inoperative software used during flight testing to exit at a critical Nr threshold and (2) the lack of distinct and unambiguous cues for low Nr.
There are currently three 525s undergoing flight testing. The Federal Aviation Administration certified the Bell 525’s CT7 engines in March 2019.
The number three Bell 525 Relentless prototype, N525BN, first flew 22 April 2016.
The prototype Lockheed C-5A Galaxy, 66-8303, at Marietta, Georgia, 30 June 1968. (Bettmann/CORBIS)Lockheed test pilot Leo J. Sullivan. (Photograph courtesy of Neil Corbett, Test and Research Pilots, Flight Test Engineers)
30 June 1968: At 7:47 a.m., Eastern Daylight Time, the first Lockheed C-5A Galaxy transport, serial number 66-8303, took off on its maiden flight at Marietta, Georgia. Chief Engineering Test Pilot Leo J. Sullivan and test pilot Walter E. Hensleigh, flight engineer Jerome H. Edwards, and E. Mittendorf, flight test engineer, made up the flight crew. U.S. Air Force test pilot Lieutenant Colonel Joseph S. Schiele was also on board.
The C-5A weighed 497,000 pounds (225,435 kilograms) at takeoff. After a 3,800 foot (1,158 meters) takeoff roll, it lifted off at 123 knots (142 miles per hour/228 kilometers per hour). It remained in takeoff configuration while it climbed to 10,000 feet (3,048 meters) at 140 knots (161 miles per hour/259 kilometers per hour). The flight lasted 1 hour, 34 minutes. On landing, the Galaxy’s touchdown speed was 116 knots (133 miles per hour/215 kilometers per hour).
Lockheed C-5A Galaxy 66-8303 during its first flight. (Code One Magazine)
The Lockheed C-5A Galaxy (Lockheed Model L-500) is a long-range, heavy lift military transport with high, “shoulder-mounted” wings and a “T-tail.” It has a flight crew of two pilots, two flight engineers and three load masters. The airplane’s cargo compartment can be accessed by a ramp at the rear of the fuselage, and the nose can be raised to allow cargo to be loaded from the front. The wings’ leading edges are swept to 25°. Four turbofan engines are mounted on pylons beneath the wings. The landing gear has 28 wheels in five units, and can “kneel” to bring the cargo deck closer to the ground for loading and unloading.
The C-5 is a truly giant aircraft. It is 247 feet, 10 inches (75.540 meters) long with a wingspan of 222 feet, 9 inches (67.894 meters) and overall height of 65 feet, 1 inch (19.837 meters). The cargo compartment has a height of 13 feet, 6 inches (4.115 meters) and width of 19 feet (5.791 meters). It is 143 feet, 9 inches (43.825 meters) long. The C-5A has a maximum takeoff weight of 840,000 pounds (381,018 kilograms) and a maximum cargo weight of 270,000 pounds (122,470 kilograms).
A McDonnell Douglas KC-10 Extender refuels a Lockheed C-5A Galaxy. (U.S. Air Force)
The C-5A, C-5B and C-5C are powered by four General Electric TF-39 high-bypass turbofan engines, rated at 43,000 pounds of thrust, each. The C-5M uses four General Electric F138 engines rated at 51,250 pounds of thrust, each.
The Galaxy has a cruise speed of 0.77 Mach and maximum speed of 0.79 Mach. Its service ceiling is 35,700 feet (10,881 meters) and its unrefueled range is 2,400 nautical miles (3,862 kilometers).
Lockheed C-5A Galaxy 66-8304, the second airplane, during a test flight near Edwards Air Force Base, California. (U.S. Air Force)
Lockheed produced 81 C-5A Galaxy transports for the U.S. Air Force between 1969 and 1973. These were followed by 50 C-5Bs. Two C-5As were modified to C-5Cs to carry larger “space cargo.” Remaining C-5s in the fleet are being modified to an improved C-5M Super Galaxy variant.
The first prototype C-5A, 66-8303, was destroyed by and explosion and fire after being defueled at Dobbins Air Force Base, 17 October 1970. One person was killed.
An M1A1 Abrams Main Battle Tank being loaded on the forward cargo ramp of a Lockheed C-5M Super Galaxy. The transport’s nose has been raised to provide loading access from the front of the airplane. The tank weighs 139,081 pounds (63,086 kilograms). (Roland Balik/U.S. Air Force)
North American Aviation Engineering Test Pilot Louis Wait with a wind tunnel model of the NA-73X. (North American Aviation, Inc.)
28 June 1940: A ¼–scale mahogany model of the North American Aviation NA-73X, prototype of the Royal Air Force Mustang Mk.1, was tested in the Ten-Foot Wind Tunnel at the Guggenheim Aeronautical Laboratory of the California Institute of Technology (GALCIT) in Pasadena, California, from 28 June to 26 July 1940.
The Ten-Foot Tunnel was funded by a $300,000 grant from the Daniel Guggenheim Foundation. Construction of the Laboratory began in 1927 and the wind tunnel became operational in November 1929. A 15 foot (4.572 meter) diameter fan was capable of producing air speeds up to 200 miles per hour (322 kilometers per hour). The first complete scale model airplane to be tested was the Northrop Alpha.
Airships, airplanes, and structures (bridges, buildings) were tested in the tunnel. According to Caltech, the Douglas Aircraft Company used the facility more than any other manufacturer.
During World War II, a staff of sixty worked three shifts, seven days a week. A technician who worked there later said, “We had a tighter schedule than the tightest schedule anyone ever had.”
The wind tunnel’s test equipment was damaged by the Whittier Narrows Earthquake. It was closed in 1997 to be replaced by a new facility.
Model builders working on a scale model wing for use in NACA’s wind tunnels. (NASA)
